Amplification of arsH Gene in Lactobacillus acidophilus Resistant to Arsenite

The aim of the study was to develop arsenite resistance in Lactobacillus acidophilus and to show the presence of arsenical resistant gene in its plasmid. The arsH gene and its homologs are fundamental to confer high level of arsenite resistance in bacteria. In the present study in vitro resistance against arsenite (up to 32 ppm) was developed in Lactobacillus acidophilus and the gene responsible for high level of arsenite resistance (arsH gene) was cloned and sequenced. Concomitantly, arsenite Minimal Inhibitory Concentration (MIC), growth phase studies, antibiotic and heavy metal tolerance were tested for this strain. The arsenite-resistant strain IITR-RKU1 showed similar growth phase patterns to that of normal parent strain in the absence or in presence of arsenite in the media. PCR using specific primers of arsH gene showed the presence of 606 bp arsH gene on a 23 kb (kilo base) plasmid of Lactobacillus acidophilus. The putative product of this gene is 202 amino acids long, having calculated molecular weight of 23 kDa (kilo Dalton) and isoelectric point of 6.0. The amino acid sequence of arsH of L. acidophilus showed 99% identity with arsenical resistance protein of Acetobacter sp. Comparison of the predicted amino acid sequence of arsH with CD (Conserved Domain) server revealed the signatures of Flavin Mono Nucleotide (FMN) reductase protein. So far arsH, in general, has been reported in Gram-ve bacterial isolates. This is for the first time arsH has been shown to be present in L. acidophilus plasmid pRKU101.